Wheelchair occupants who remain in a fixed position for prolonged periods of time encounter trauma to the skin tissue or pressure sores. This trauma is a result of a constant pressure applied to the wheelchair occupant's person. The pelvis area or region of the wheelchair occupant is especially susceptible because the bones in the pelvis region are substantially sharp. Continuous pressure of the wheelchair seat cushion against the wheelchair occupant induced by the wheelchair occupant's weight pinches the skin in the pelvis region between the seat cushion and the bones in the pelvis region. The continuous pressure and the substantially sharp bones make the skin in the pelvis area highly prone to trauma.
To reduce the risk of trauma to the skin, the wheelchair occupant's body may be shifted periodically. This changes the weight distribution of the wheelchair occupant, which, in turn, changes the points of pressure against the wheelchair occupant's person. Wheelchair occupants, however, are often disadvantaged in that they do not have the ability to shift their own weight because of their immobility. To meet the needs of the wheelchair occupants, tilt systems have been devised to tilt the wheelchair seat, and thereby shift the weight of the wheelchair occupant.
Early wheelchair seat tilt systems were manually operated requiring the aid of one or more attendants to assist the wheelchair occupant in tilting the wheelchair seat. This did not satisfy the needs of the wheelchair occupant to the extent that the wheelchair occupant still required assistance to tilt the wheelchair seat.
More recent innovations in wheelchair seat tilt systems have led to automated tilt systems. Automated tilt systems generally include a wheelchair seat frame that is pivotally supported by a wheelchair base. The base typically includes a pair of spaced apart side frames. The wheelchair seat spans between the side frames. The wheelchair seat is generally provided with a rear laterally extending cross tube. The cross tube has opposing ends. These opposing ends pivotally engage the spaced apart side frames. The seat frame further includes side tubes and a front cross tube. The front and rear cross tubes and the side tubes are triangulated to form a rigid seat frame. Most conventional seat frames include a clevis on the front of the base frame and a clevis on the front of the seat frame for receiving opposing ends of a linear actuator. The actuator is extended and contracted by a motor. Contracting the actuator causes the front end of the seat frame to rise upwards, and extending the actuator causes the seat frame to lower back down.
This arrangement was originally problematic in that the actuator provided the sole support for the front end of wheelchair seat. This was not the most stable environment for the wheelchair occupant. To overcome this instability, braces were provided to support, or to provide supplemental support, for the wheelchair seat. The braces most often appear on opposing sides of the seat frame. The braces usually have a lower end pivotally attached to the wheelchair base and an upper end pivotally attached to the seat frame.
Until the more recent past, a common problem that remained in wheelchair tilt systems was associated with the center of gravity of the wheelchair occupant. Most tilt systems employed a fixed pivot axis upon which the wheelchair seat was tilted. As the wheelchair seat tilted back the wheelchair occupant's center of gravity shifted. This shift in the center of gravity was undesirable because it is most desirable to maintain the wheelchair occupant's center of gravity in an area over and between the front casters and the rear or drive wheels of the wheelchair. Distributing the wheelchair occupant's center of gravity in this area provides optimum control over the wheelchair and reduces the risk of the wheelchair's inadvertently tilting forwardly or rearwardly over. To meet this need, wheelchair seat frames have been mounted to the wheelchair base on a movable pivot that moves forward as the seat frame is tilted back. This maintains the wheelchair occupant's center of gravity in an area above and between the front caster and the drive wheels of the wheelchair. To facilitate the movement of the seat frame pivot points, an intermediate frame is employed. The intermediate frame is a bulky frame structure that is fixedly attached to the top of the wheelchair base. The intermediate frame has opposing side each of which embody a sliding pivot. The seat frame is coupled to the sliding pivot. As the seat frame is tilted back, the seat frame slides forward relative to the intermediate frame, shifting the wheelchair occupant's center of gravity forward to maintain the wheelchair occupant's center gravity between the front casters and the drive wheels of the wheelchair.
Although wheelchairs have made leaps in a direction to meet needs of the wheelchair occupants, improvements in wheelchairs have resulted in complicated and cumbersome configurations, such as, the intermediate frame structure used to accomplish the shift in the wheelchair occupant's center of gravity as the wheelchair seat frame tilts back. Conventional tilt systems are inefficient and expensive, in part, because of the complicated and cumbersome configurations. Costly tilt systems have provided little benefit to wheelchair occupants who struggle financially to meet their healthcare needs. What is needed is a more simplistic wheelchair seat tilt system that may be provided at a lower cost to the wheelchair occupant.